The present invention relates to a chemical sensing system, and more particularly to a sensing system that utilizes two ion-separation technologies in tandem to detect specific chemicals in the presence of common environmental chemical backgrounds.
Sensing to identify and quantitate specific chemicals is of interest for a variety of purposes, including assuring human safety in environments that may contain threats from Toxic Industrial Chemicals (TICs) or Chemical Warfare Agents (CWAs), and in industrial process control. Chemical sensing for environmental monitoring must be compatible with safety requirements, as specifically promulgated by OSHA and other government organizations through time-weighted average Permissible Exposure Limits (PELs). These standards are also broadly applied to potential chemical threats. Many TICs, including pesticides, acid vapors, and carcinogens, and the CWAs have PELs that range from part per million (ppm) and part per billion (ppb) levels to part-per-trillion (ppt) levels in air. At those low concentrations the air we breathe can have hundreds of other chemicals (scents, simple hydrocarbons, and other non-toxic vapors) in addition to near percent loads of water and carbon dioxide. Similarly, industrial process streams may have the chemicals to be monitored embedded in complex mixtures. Accurately and sensitively detecting the compounds of interest in the presence of complex and variable chemical backgrounds has historically required advanced laboratory analytical separations and complex instrumentation, such as gas chromatograph-mass spectrometry (GC-MS). GC-MS is a tandem or “hyphenated” analytical technique that represents a laboratory level standard for chemical mixture analysis, where the resolving power of two “orthogonal” measurement techniques that respond to different physical/chemical properties is used to extract signals from a complex sample matrix.
There is a looming possibility that civilians and first responders may be exposed to environments involving hazardous chemicals including CWAs. Low-cost portable and fixed site sensors providing reliable detection of TICs and CWAs at ppb and sub-ppb levels are required to provide rapid, on-site characterization and warning of the threat in the event of an attack or incident. No portable sensor technology exists that can detect specified lists of TICs and CWAs at the sub-ppb levels in real time and with acceptable false-alarm rates in the presence of common environmental chemical backgrounds.
Variations of Ion-Mobility Spectrometry (IMS) have been utilized for chemical vapor detection. The variants include Time-of-Flight IMS (TOF-IMS), Radio Frequency IMS (RFIMS), and a technique known either as Field Asymmetric IMS (FAIMS) or Differential Mobility Spectrometry (DMS). As with TOF-IMS, the FAIMS and DMS variants are highly sensitive with moderate specificity. However, both TOF-IMS and DMS are increasingly subject to false detection as sensor gain is increased and sub-ppm limits of detection are pursued, this due to the more complex nature of samples at ppb and ppt levels. While DMS technology has the sensitivity to approach PEL level detection of CWAs without preconcentration, resolution becomes a limiting factor in the presence of trace environmental chemical backgrounds.
Accordingly, it is desirable to provide a chemical sensing system that detects specified lists of TICs and CWAs at the sub-ppb levels in real time and in the presence of common environmental chemical backgrounds.